GB952570A - Data transmission apparatus - Google Patents

Abstract

952,570. Telegraphy. WESTERN ELECTRIC CO. Inc. Sept. 20, 1962 [Sept. 29, 1961], No. 35794/62. Heading H4P. A telegraph receiver comprises means for responding to a received first condition signal, control means responsive to said means for responding for connecting the receiver means via signal inversion means to the means for responding whereby the latter becomes responsive to disable the receiver when signals are no longer being received. As shown, a plurality of sets of transmitter receiver equipment are connected to the public telephone system. Each set (Fig. 6) includes a telephone receiver and dial 604. An attendant at the originating station dials the number of a called station. If the called station is attended the two operators communicate in the usual manner using the teleprinters 603. The originating station sends its messages using mark and space frequencies F 1m , F 18 , respectively, and the called station sends replies using higher frequencies F 2m , F 2s . If the called station is unattended a control and logic circuit 605 waits one second under the control of a timer 610 then directs an answer back generator 620 to send a mark frequency F 2m corresponding to the letter " V " to indicate that it is ready to receive a message. In response to this signal the originating station should then send a message using the frequencies F 1m , F 1s . These frequencies when received at the called station are amplified at 607, passed through an appropriate band of a filter 614 and after being limited at 616 and inverted at 619 are fed to the timer 610 and to the teleprinter keyer circuit 622. The timer 610 is arranged to time each of the space frequencies F 1s to see if any of them are of more than one second duration. If this occurs it is assumed that the message is complete and the teleprinter switches off. This will also happen if no signal is received or if the signal is too weak. For test purposes the operator of a set may call up a test station and if required may first depress a disconnect key followed by an answering key to cause the test station to automatically take over as the originating station, i.e. the frequencies F 1m , P 1s are used instead of F 2m , F 2s and vice versa. Specifications 676,779 and 677,191 are referred to.